Standard error of radar estimated precipitation as a function of distance and intensity

The NWS's WSR-88D employs an algorithm to correlate radar reflectivity to surface rainfall amounts. It is understood that these amounts are not completely accurate and the degree of error increases with distance away from the WSR-88D due to the level at which the radar beam is set. This research focuses on calculating the level of error as a function of distance away from the radar location and amount of precipitation. The research will consist of placing the Vaisala WXT-510s at 25km increments in a radial direction from the location of the radar site. Rainfall rates and rainfall amounts will be measured over a period of one month using the WXT-510s. After each precipitation event has passed, the data from the WXT-510s will be compared to the output from the WSR-88D. During this same period the DOW Radar Observations at Purdue study (DROPs, 21 October - 18 November 2009) will be conducted on campus and additional measurements will be taken as an added verification for precipitation amount.

The analysis of the error from the WXT-510s and the WSR-88D will be done using a mean standard error, standard deviation, root mean square error, and correlation between instrument precipitation amounts. Specific emphasis and analysis will be placed on the degree of error compared to the distance from the radar site and the degree of error compared to the amount of rainfall. From the research, we hope to provide information to the NWS's WSR-88D algorithm for precipitation amount. This research will not only benefit the NWS, but also the general public and agricultural industries to which rainfall accuracy is imperative.